The invention relates to a disk brake and a brake pad set for a disk brake.
Such disk brakes are required in the vehicle sector. It is common practice to configure the friction linings fastened to the carrier plates of the brake pads with bevelled faces, i. e. not with surfaces extending parallel to the brake disk or the carrier plate.
The brake pads fixed on either side of the disk brake have friction linings with bevelled surfaces of mirror-inverted arrangement.
Disk brakes are complex, oscillatory systems which are excited to oscillate by the friction forces acting in the contact surfaces between the friction linings and the brake disk.
On of these oscillation problems is the so-called creaking of brakes. This phenomenon is due to low-frequency oscillations in the frequency range from approximately 20 to 150 Hz occurring during the transition from adherence to friction and at an extremely low velocity of the vehicle. Creaking of the brakes occurs in particular in high-duty vehicles with automatic gearbox due to the driving torque being permanently applied to the drive shaft.
In the past few years oscillation problems have to a growing extent been encountered in the automotive sector. One reason for this is the consequent realization of light-weight construction and cost reduction concepts. On the other hand, the vehicle buyers make increasing demands on the comfort to be offered by a vehicle and require the disturbing driving noises to be eliminated.
The so-called slip stick effect is blamed for the occurrence of the creaking noises. The slip stick effect is the alternate adherence and sliding of the friction linings to/on the brake disk.
In the vehicle creaking occurs in two different situations. A typical case, which frequently occurs in high-duty vehicles with automatic gearbox, is release of the vehicle brake with a driving torque being applied. If a driving torque acts upon the drive shaft while a vehicle stands still with the brake being applied, slow release of the brake may cause a clearly audible crack or even a penetrating buzzing noise. The driving torque needs not necessarily be generated by the engine, it may also be produced by a gravitational force occurring when the vehicle is in downhill position. In this case, too, the brake creaks if it is slowly released and a certain critical contact pressure of the brake lining has been reached. The buzzing noise described may occur during uniform and slow movement of the vehicle and constant contact pressure for an extended period of time.
Even when the vehicle is braked at higher velocities a short creaking noise may be audible during the transition from friction to adherence immediately before the vehicle stops.
It is the object of the invention to provide a disk brake or a brake pad set for a disk brake by means of which occurrence of low-frequency noises is to be prevented.
The invention provides in a preferable manner for the friction linings of the brake pads to comprise areas of reduced layer thickness which are not of mirror-inverted arrangement in the brake pads in relation to the brake disk. Since the friction linings relative to a plane in the brake disk are not arranged mirror-symmetrically, either side of the brake disk presents different frictional forces thereby inducing different oscillations on either side of the brake disk, which affects the self-excitation of the oscillation and thus the suppresses occurrence of low-frequency oscillations in the frequency range from 150 Hz, and in particular resonance phenomena.
The bevelled friction linings are configured so that the areas of reduced layer thickness have a surface inclined towards the carrier plates and incline, e. g. at an angle of approximately 10 to 45xc2x0 to the carrier plate, tangentially to the outside in the direction of the carrier plate.
The separating line between the areas of the friction lining layer with identical layer thickness and the areas of reduced layer thickness may extend in parallel to the symmetrically bisecting line of the brake disk, which extends in radial direction of the brake disk, or at an angle to said symmetrically bisecting line. The angle to said symmetrically bisecting line may be in the range from xc2x10 to 60xc2x0, preferably in the range between xc2x110 and 30xc2x0.
For example, in the case of brake pad pairs located opposite each other it is envisaged that said separating line extends in opposite direction on both sides of the brake disk and thus not mirror-symmetrically.
Hereunder embodiments of the invention are explained in detail with reference to the drawings in which: